Sometimes, the best defense is a good offense. Renee Zellweger must not want to be seen as the sad sack dumpee in her recent split from Bradley Cooper, because she went out of her way this weekend to put on a happy face.

On Saturday, the squinch-expression-prone Oscar winner slipped out of her de rigueur workout clothes and into a sexy ensemble to celebrate a friend's birthday at a New York restaurant, reports Us.

So hot that a trio of waiters "came up to see if the table needed anything because they wanted to check out Renee," continues the suspiciously pro-Zellweger eyewitness, who doesn't seem to entertain the possibility that the staffers were just hoping for a big tip from the famously generous star.

The next night, Zellweger was "beaming" and laughing during the Broadway opening of "Priscilla, Queen of the Desert," reports the New York Post.

Once again sheathed in a black dress, the actress enjoyed the drag-queen-a-riffic show with a galpal, telling the paper at intermission, "I am really having a good time."

Translation: She's not dwelling on the end of her nearly two-year, live-in romance with Cooper, even amid tabloid rumblings that he'd wanted out for a while and may have been considering other A-list romantic possibilities.

"She tried to make it work, but in the end it was too hard," a Zellweger insider tells Us. "Her friends feel bad it ended, but she's okay."

Meanwhile, PopEater believes it was Renee's desire to take the relationship to the next level that caused it to run off the rails.

A source claims that after supporting the newly crowned box office champ through the death of his father in January, "She wanted a ring, and he just wasn't ready to propose."

Sighs the pal, "They were such a great couple that we are all shocked. We all thought for sure they were going to be together forever after they moved in together last fall -- we're really sad."

Another supposed sticking point was their marital track records, with both experiencing unions that lasted only four months (he swapped vows and parted ways with Jennifer Esposito in 2007; she annulled her 2005 marriage to Kenny Chesney, citing fraud).

"There is no doubt both of these people have not had a great experience being married," the spy tells PopEater. "Renee was ready to give it another try with Bradley. She's 41 and has an Oscar. She's starting to think about children and settling down while Bradley loves his life exactly as it is. It's taken him a long time to be an A-list actor, and he's enjoying all the perks, fame and opportunities that have come his way following 'The Hangover.'"

Concludes the source, "They are both in very different places in their lives and unfortunately just grew apart."